Marking apparatus and method for operating a marking apparatus

ABSTRACT

The invention relates to a marking apparatus for marking an object comprising a marking head having a plurality of receiving spaces for individual marking devices, wherein the receiving spaces are arranged in a plurality of rows and columns, such that a two-dimensional array of receiving spaces is formed, and a driving mechanism for providing a relative movement of the object relative to the marking head in an advance direction during a marking operation. The marking head is rotatable about an axis extending transversely to the advance direction, at least one detector device is arranged downstream of the receiving spaces in the advance direction, and a control marking, which has been applied by at least one marking device arranged in one of the receiving spaces during the movement of the object relative to the marking head, is detectable by the at least one detector device at different angles of rotation of the marking head. The invention further relates to a method for operating a marking apparatus.

The present invention relates to a marking apparatus for marking anobject according to the preamble of claim 1. The invention furtherrelates to a method for operating a marking apparatus, according toclaim 10.

The marking apparatus comprises a marking head having a plurality ofreceiving spaces for individual marking devices. The receiving spacesare arranged in a plurality of rows and columns, such that atwo-dimensional array of receiving spaces is formed. The apparatusfurther comprises a driving mechanism for providing a relative movementof the object relative to the marking head in an advance directionduring a marking operation.

In a known marking apparatus the receiving spaces and the markingdevices, respectively, are arranged in a fixed pattern so that themarking apparatus has a defined resolution.

When a marking operation is carried out, the object is moved in theadvance direction relative to the marking head and a marking is appliedon the object by means of marking devices arranged in the receivingspaces of the marking head. The marking can in particular be applied onthe object during the relative movement between the object and themarking head.

In order to achieve a good marking quality it is necessary to correctlyadjust the position of the marking head relative to the movementdirection of the object. If the actual advance direction of the objectis slightly tilted relative to a desired advance direction or theposition of the marking head is not correctly adjusted relative to theadvance direction the marking quality might be reduced.

It is an object of the invention to provide a marking apparatus and amethod for marking an object with a high marking quality.

The object is solved according to the invention with a marking apparatushaving the features of claim 1. The object is further solved accordingto the invention with a method having the features of claim 10.Preferred embodiments of the invention are given in the dependentclaims.

The inventive marking apparatus is characterized in that the markinghead is rotatable about an axis extending transversely to the advancedirection. Moreover, at least one detector device is arranged downstreamof the receiving spaces in the advance direction, and a control marking,which has been applied by at least one marking device arranged in one ofthe receiving spaces during the movement of the object relative to themarking head, is detectable by the at least one detector device atdifferent angles of rotation of the marking head.

The inventive method comprises the steps: the object is moved relativeto the marking head in the advance direction, a control marking isapplied by the at least one marking device during the movement of theobject relative to the marking head, and the control marking is detectedby a detector device which is arranged downstream of the at least onemarking device. The marking head to be operated by the inventive methodcomprises a plurality of receiving spaces for individual marking devicesfor marking the object, the receiving spaces being arranged in aplurality of rows and columns, such that a two-dimensional array ofreceiving spaces is formed. At least one receiving space is equippedwith a marking device. The marking head is rotatable about an axisextending transversely to the advance direction.

A first fundamental idea of the invention is to provide a markingapparatus and method with an adjustable marking resolution. To this end,the array of marking devices is arranged in a rotatable manner in themarking apparatus. Accordingly, the resolution of the marking can bechanged by rotating the array of marking devices, in particular about arotation axis extending perpendicular to a surface of the object to bemarked and/or perpendicular to the advance or movement direction of theobject. The marking resolution can be adjusted to a given marking taskand therefore increase the marking quality.

A second aspect of the invention is to provide a method for determiningan angle of rotation of the marking head and/or for setting up a definedangle with a desired marking resolution, taking into account inparticular the actual movement direction of the object relative to themarking head. The angle of rotation may also be referred to as arotation angle or a tilt angle.

In order to determine the actual angle of rotation of the marking head acontrol or reference marking may be applied by one or more of themarking devices during a movement of the object relative to the markinghead. The control marking, which may in particular be a marking line,can be detected by the detector device. As the control marking isapplied during a movement of the object relative to the marking head,the control marking extends in the advance direction.

Depending on the rotation angle of the marking head the position of themarking is displaced in the transverse direction. That is, the positionof the marking in the transverse direction depends on the rotation angleof the marking head, provided that the marking device is arrangedeccentrically on the rotatable marking head. The rotation angle of themarking head can in particular be defined as an angle between a columnof marking devices in the marking head and the actual advance directionof the object.

Hence, the position where the control marking is detected corresponds tothe rotation angle of the marking head. If the position of the controlmarking is known, it is therefore possible to determine the rotationangle of the marking head.

Therefore, for example, the inventive apparatus and method can be usedfor determining the rotation angle of the marking head.

In addition, the apparatus and method provides a possibility to set up adefined rotation angle of the marking head with a predetermined markingresolution. The predetermined marking resolution can in particular bedefined as a marking resolution having a predetermined characteristic.The predetermined marking resolution can for example be a markingresolution which allows for marking continuous lines in the transversedirection, in particular in a direction extending perpendicular to theadvance direction of the object.

When the rotation or tilt angle of the marking head is 0° the resolutionis generally defined by the pitch or distance of the receiving spaces ofone row. The tilt angle of 0° is in particular given if the columns ofthe receiving spaces are aligned with the advance direction and/or therows of the receiving spaces extend perpendicular to the advancedirection.

The resolution can be enhanced by tilting or rotating the marking head.If the marking head is only tilted a very small angle, the markingresolution might not be constant for the entire marking head, as theremight be larger gaps between two adjacent columns of marking devices inthe transverse direction. If the marking head is tilted too much, themarking resolution might be too poor to mark a continuous line in adirection perpendicular to the advance direction.

The invention provides an apparatus and a method for determining andsetting up a maximum rotation angle with which a continuous marking linein a direction perpendicular to the advance direction can be applied onthe object.

To this end, marking is applied on the object by a plurality of markingdevices arranged in one row of the marking head. As the row is tiltedwith regard to the advance direction, the marking will be a wide markingline that may also be called a marking bar. The wide marking line has awidth wider than a marking applied by a single marking device. The widthwill in particular be defined by a spacing of a first and a last markingdevice in the column.

The marking bar can be detected and analyzed. Based on the analysis ofthe marking bar certain characteristics of the marking can bedetermined. It is in particular possible to determine if the set up tiltangle is appropriate for marking a continuous line at right angles tothe advance direction of the object

According to the invention it is fundamental to know the position of theat least one detector device relative to the position of the at leastone marking device which applies the control marking. It is thereforepreferred that the detector device is arranged within the marking head,in order to eliminate as much as possible any factors that might impairthe defined, known position of the detector device relative to themarking device.

In order to provide the possibility to detect the control marking whilethe object is moved relative to the marking head, it is preferred thatthe at least one detector device is arranged downstream of the receivingspaces in the advance direction.

A fundamental aspect of the inventive marking apparatus is the fact thatthe at least one detector device is configured to allow for a detectionof the control marking at various different rotation angles of themarking head. The detector device therefore needs to cover a distance inthe transverse direction being significantly larger than a width of acontrol marking line applied.

The at least one detector device preferably covers a substantial portionof the marking width of the marking head, for example at least 80 or 90%of the marking width of the marking head. More preferably, the detectordevice covers at least the entire marking width of the marking head, inparticular a width corresponding to a length or width of one row ofreceiving spaces.

In order to provide the possibility to detect the control marking atdifferent angles of rotation of the marking head, one single detectordevice may be configured to cover a width in the transverse directionbeing larger than a width of a marking applied by a marking device.

It is also possible to provide a plurality of detector devices arrangedin an array covering a width in the transverse direction being largerthan a width of a marking applied by a marking device.

In a particularly preferred embodiment the at least one detector deviceis movable along a defined movement path relative to the receivingspaces of a marking head, in order to cover a width being larger than awidth of a marking applied by a marking device. In a preferredembodiment the movement path is arranged in the marking head.

The movement path may in particular extend in a transverse directionwith regard to the advance direction and/or substantially parallel to arow of receiving spaces of the marking head and/or substantiallyperpendicular to a column of receiving spaces of the marking head.According to a preferred embodiment, the at least one detector device istherefore movable in a transverse direction relative to the advancedirection.

For moving the detector device along the movement path it is preferredthat a slider or carriage is provided on which the detector device isarrangeable and which is movable with regard to the receiving spaces ofthe marking head. A drive unit comprising a motor can be provided formoving the slider.

The at least one detector device is preferably movable along the definedmovement path such that, at different angles of rotation of the markinghead, it may be placed in a position in which it is aligned in theadvance direction with regard to at least one of the receiving spaces.

In a preferred embodiment the at least one detector device is movablealong a linear movement path. The linear movement path may in particularextend parallel to the rows of receiving spaces and/or perpendicular tothe columns of receiving spaces. The linear movement path facilitates aprecise movement and an exact positioning of the detector device.

It is preferred that a measuring device is provided for determining theposition of the detector device detecting the control marking. Themeasuring device may in particular be configured to determine theposition of the movable detector device at a time when the controlmarking is detected by the detector device. Therefore, the position ofthe control marking can be known based on the time when the controlmarking is detected by the moving detector device. Based on the positionof the control marking and/or the detector device the rotation angle ofthe marking head can be determined.

In another preferred embodiment a processing unit is provided fordetermining a value of an angle of rotation based on the detectedcontrol marking. The processing unit may in particular have as an inputvalue a position of the detected control marking.

In another preferred embodiment a processing unit is provided fordetermining a characteristic of the detected control marking. Theprocessing unit may in particular be functionally connected to the atleast one detector device. The characteristic of the detected controlmarking may in particular relate to the position of the control markingand/or the resolution of the control marking, in particular if thecontrol marking is applied by a plurality of marking devices.

According to the invention the receiving spaces of the marking head andthe marking devices coupled thereto are arranged in a two-dimensionalarray comprising rows and columns. The two-dimensional array may inparticular be employed for an enhancement of the marking speed and/orthe marking resolution, as already explained. The receiving spaces ofthe marking head can be entirely or partially equipped with markingdevices.

According to the invention the two-dimensional array of receiving spacesand marking devices, respectively, is rotatable or tiltable about anaxis extending transversely, in particular at right angles, to theadvance direction and/or to a surface of the object to be marked.

Through the rotation of the array, the array can be arranged in aposition, in which the receiving spaces of a successive row are offsetwith regard to the receiving spaces of a preceding row in the transversedirection. In other words, the receiving spaces of a successive row maybe interposed between receiving spaces of a preceding row in the advancedirection. Such a staggered arrangement of the receiving spaces,respectively marking devices, increases the marking resolution. Thesmaller the offset and the greater the number of rows, the greater isthe resolution to be achieved.

For a precise movement of the marking head it is preferred that a motor,in particular a stepper motor, is provided for rotating the markinghead, in particular at defined small angle steps in the range of 0 to 90degrees. The small angle steps are in particular steps of less than 1degree, preferably less than 0.1 degrees. The motor may in particular bean electrical motor. The motor may in particular be controlled based onan output value of the processing unit.

In a preferred embodiment the array of receiving spaces is an orthogonalarray, in which the receiving spaces are arranged in rows and columnsextending perpendicularly to each other. In such an orthogonal array thereceiving spaces are arranged in a rectangular pattern. The orthogonalarray can be easily fabricated and generally provides a very goodresolution.

It is preferred that the receiving spaces of the array have an equalspacing in a row direction and/or in a column direction. In other words,a pitch of the receiving spaces in the row direction and/or the columndirection is preferably equal throughout the array. The equal pitchallows for a constant marking resolution throughout the array.

The marking apparatus may for example be a printing apparatus, inparticular for printing or engraving an object by means of at least onelaser beam. The marking apparatus can particularly be configured for asuccessive marking operation, in which the object is marked by aconsecutive operation of the individual marking devices, that is, theobject is marked line by line or pixel by pixel, in particular while theobject is moved relative to the marking head.

The marking devices may in particular be marking devices for marking,printing and/or engraving the object with at least one laser beam.However, the marking devices can also include inkjet nozzles, thermalprinting devices, needle printing devices, micro pad printing devices,water jets, electrical discharge machining devices and/or any othertypes of marking devices. It is also possible to include different typesof marking devices in the marking head.

The at least one detector device may in particular be an optical sensordevice and may comprise for example a PIN diode, a photo diode, a photosensor or a photo transistor, for sensing or scanning the object.

It is preferred that for detecting the control marking on the object,light is transmitted to the object, the light is at least partlyreflected and/or scattered by the object and the reflected and/orscattered light is detected by a sensor element. The light may bevisible light, infrared light and/or any other type of electromagneticradiation.

In a preferred embodiment a marking device and/or a detector devicecomprises a ferrule with at least one fibre arranged therein. In case ofa marking device, the fibre may be coupled to a laser device. In case ofa detector device, the fibre may be coupled to a sensor element.

In a preferred embodiment the receiving spaces of the marking and/orscanning head are receiving holes formed in a receiving plate. Thereceiving holes may in particular be through-holes. The marking devicesmay be inserted into the receiving holes and thereby coupled to thereceiving plate.

Regarding the inventive method it is preferred that the detector deviceis moved in a transverse direction relative to the advance direction andthe control marking is detected by the detector device during themovement of the detector device in the transverse direction.

The control marking can for example be analysed. It is particularlypreferred that a width or brightness of a control marking line isdetermined.

In another preferred embodiment of the method an angle of rotation ofthe marking head is determined based on the control marking.

In yet another preferred embodiment a plurality of receiving spacesarranged in one column is equipped with a marking device the markinghead is arranged in a tilted position in which the column of markingdevices is inclined with regard to the advance direction of the object acontrol marking is applied by the plurality of marking devices duringthe movement of the object relative to the marking head, which controlmarking is a wide control bar due to the tilted position of the markinghead, and the control bar is detected by the detector device, which isarranged downstream of the marking devices. It is particularly preferredthat the control bar is analyzed. For example, the resolution of thecontrol bar may be determined. Based on the determined resolution thetilt angle of the marking head may be adjusted in order to achieve adesired resolution.

The invention will now be further described with reference to theattached figures, wherein:

FIG. 1 shows a marking apparatus according to the invention;

FIG. 2 shows a general perspective view of a marking head according tothe invention;

FIG. 3 shows a marking head according to the invention and a firstmethod for operating the marking head;

FIG. 4 shows detecting signals detected by the detector device in thefirst method;

FIG. 5 shows the marking head according to FIG. 3 and a second methodfor operating the marking head;

FIG. 6 shows detecting signals detected by the detector device in thesecond method and

FIG. 7 shows a cross-sectional view of an inventive marking head.

In all figures, identical components are identified by identicalreference signs.

The principal structure of a marking apparatus 10 according to theinvention is shown in FIG. 1. The marking apparatus 10 comprises amarking head 20 with a plurality of marking devices 40. The apparatus 10further comprises a control and driving unit 12 for controlling themarking devices 40. The control and driving unit 12 is connected to themarking head 20 through an umbilical 14. The umbilical 14 may have aplurality of fibres arranged therein. The marking head 20 may inparticular be a printing head and may have a cylindrical housing 21.

Additional features of the marking head 20 are shown in FIGS. 2, 3, 5,and 7. The marking head 20 includes a plurality of receiving spaces 24that may be equipped with individual marking devices 40. The receivingspaces 24 are arranged in a two-dimensional array 22 having asubstantially rectangular outer shape.

The receiving spaces 24 are arranged in rows 30 and columns 32 extendingperpendicularly to each other. The receiving spaces 24 are thus arrangedin a rectangular or square pattern, which may also be called a matrix,in particular a two-dimensional matrix.

The receiving spaces 24 have equal distances or an equal spacing, sothat a regular pattern is formed. The spacing between two adjacentreceiving spaces 24, more particularly the distance between the centralpoints of two adjacent receiving spaces 24 in one row, is called a rowpitch. Accordingly, the spacing between two adjacent receiving spaces inone column 32 is called a column pitch. The receiving spaces 24 haveequal row pitches and equal column pitches.

In the shown embodiment the marking head 20 is rotated to a degree inwhich the receiving spaces 24 of one column 32 are tilted or inclinedwith regard to a movement direction 16 of an object 80 to be marked. Themovement direction is called an advance direction 16 of the object 80relative to the marking head 20.

FIG. 7 shows a cross-sectional view of an inventive rotatable markinghead 20. The marking head 20 includes a receiving plate 28 having aplurality of receiving holes 26 forming the receiving spaces 24. Thereceiving plate 28 may for example be a metal plate, in particular asteel plate. The receiving holes 26 each have a substantially circularcross-section and may in particular be through-holes. The receivingholes 26 each have equal diameters.

In addition to the array 22 of receiving spaces 24, a plurality of sparereceiving spaces 25 is provided for accommodating spare marking devices41. The spare receiving spaces 25 are also formed as receiving holes inthe receiving plate 28.

The marking devices 40 each comprise a ferrule 42, in which at least onefibre end of a fibre 46 is arranged. The ferrule 42 is configured for amating engagement with the receiving holes 26 of the marking head 20 andmay in particular have a substantially cylindrical body 43 with acylindrical connecting portion 48 for engaging the receiving hole 26.The body 43 comprises a collar 44 with an abutment surface 45 forcontacting a planar surface of the receiving plate 28. In a preferredembodiment the body 43 of the ferrule 42 includes a metal, a ceramic, aplastic material or glass. It is particularly preferred that the ferrule42 includes steal or zirconia.

The at least one optical fibre 46 is arranged in the ferrule 42 along alongitudinal axis of the ferrule 42. The fibre 46 may be configured totransmit a laser beam onto a surface of the object 80 for a lasermarking operation, in particular a laser engraving operation. To thisend, the fibre 46 may be coupled to a laser so that a laser beam istransmittable through the fibre 46 onto a surface of the object 80 formarking the object 80.

The marking head 20 comprises a shielding device 66 for shieldingradiation from a zone between the marking head 20 and an object 80 to bemarked. The shielding device 66 comprises an inner brush ring 67 and anouter brush ring 68.

A motor 62, in particular a stepper motor, is arranged for rotating themarking head 20 and/or the receiving plate 28 relative to a base 11. Atransmission 64, which in the shown embodiment is a belt, is arrangedbetween an output shaft or a driving pulley 63 of the motor 62 and themarking head 20 for transmitting a rotational motion of the output shaftto the marking head 20 and/or the receiving plate 28.

The marking head 20 further comprises a detecting unit 70 with adetector device 50. The detector device 50 can include an optical sensorelement. In a preferred embodiment the detector device includes aferrule with an optical fibre coupled to the sensor element. The ferruleof the detector device 50 may be configured as described in connectionwith the marking device 40.

The detector device 50 is mounted on a slider 72 which is movable withregard to the array of receiving spaces 24 of the marking head 20. Thereceiving plate 28 can have a cut out in which the slider 72 or carriagecan be moved. A drive unit 74 is provided for moving the slider 72. Thedrive unit 74 comprises a spindle drive with a threaded rod or spindle78. The spindle 78 is connected to a motor 76, in particular a steppermotor, for rotating the spindle 78.

As shown, the detecting unit 70 can also have a second or spare detectordevice 51 arranged on the slider 72.

Embodiments of the inventive method will now be described with referenceto FIGS. 3 to 6. The inventive method can be called a calibrationmethod.

A first embodiment of the inventive method is illustrated in FIGS. 3 and4. The first method can be used for determining a rotation or tilt angle38 of the marking head 20 relative to the advance direction 16 of theobject 80 to be marked or printed. It is useful to carry out this methodafter an installation of the marking head 20 or after an object change.

According to the method a single marking device 40 of the marking head20 is activated and applies a marking called a reference or controlmarking 84 onto the object 80. The activated marking device 40, whichmay also be called a control marking device 40 a, is preferably amarking device 40 arranged in a top row 30 a of the marking head 20,that is, a first row 30 a in the advance direction 16. The columnposition of the activated marking device 40 is identified by the line 32a. Other marking devices 40 of the marking head 20 will be deactivatedduring the carrying out of the method.

The object 80 is moved in the advance direction 16 while the controlmarking device 40 a applies the control marking 84 on the object 80. Thecontrol marking 80 can in particular be a control marking line.

The detector device 50 is moved along a defined movement path 36 in atransverse direction 18, parallel to the rows 30 of the receiving spaces24. When the detector device 50 passes the control marking 84, thismarking is detected. Due to the known position of the detector device 50relative to the control marking device 40 a, the tilt angle 38 of themarking head 20 can be calculated.

FIG. 4 shows a detector signal 90 of the detector device 50, inparticular a signal amplitude over a slider or detector device position,when the detector device 50 detects the control marking line 84. Theupper line shows a signal 90 of the detector device 50 when a dark lineis detected on a bright background. The lower line shows a signal 90 ofthe detector device 50 when a bright line is detected on a darkbackground. The minimum and maximum, respectively, of the signal 90determines the marking line centre 86.

The position of the control marking line is identified by the dottedline 86. The column position of the activated marking device 40 a isshown by the dotted line 87. A distance between the lines 86 and 87corresponds to an actual rotation or tilt angle 38 of the marking head20. In addition the marking line width 88 can be determined based on thesignal shape.

In a corresponding manner a power of a marking device 40 can becalibrated with the inventive marking apparatus 10. The optimal power ofa marking device 40 can in particular depend on the substrate, i.e. theobject 80, to be marked. When the control line starts to appear in thesignal the minimum power requirement is set for the current substrate.When the detected line does not get wider or darker, the maximum powerrequirement is set for the current substrate.

A second embodiment of the inventive method is illustrated in FIGS. 5and 6. The second method can be used for determining an optimal tiltangle 38 of the marking head 20 relative to the advance direction 16,wherein the optimal tilt angle 38 can be a maximum tilt angle 38 inwhich a solid line may be marked in a perpendicular direction relativeto the advance direction 16.

A plurality of marking devices 40 a of one column 32 a of the markinghead 20 is activated and a control marking 84 is applied on the object80 during a movement of the object 80 in the advance direction 16. Thedetector device 50 is moved along a defined movement path 36 in atransverse direction 18, parallel to the rows 30 of the receiving spaces24. When the detector device 50 passes the control marking 84, thismarking is detected.

After the detection of the control marking 84 the tilt angle 38 of themarking head 20 is changed, in particular increased. The detector device50 is then again moved and the control marking 84 is again detected. Dueto the increased tilt angle 38, the width 88 of the control marking 84increases.

The above described steps can be repeated. That is, after each sliderpass, or detector device pass, the tilt angle 38 of the marking head 20is slightly increased. Therefore the slider 72 and/or the detectordevice 50 performs an oscillating movement, as shown by the arrow 37.

Different detector signals referring to different tilt angles 38 areshown in FIG. 6. As in FIG. 4, the figure shows a signal amplitude overa slider or detector position.

A first detector signal 92 refers to a relatively small first tiltangle. With an increasing tilt angle the line signal width increases.For example, a second detector signal 94 refers to a tilt angle which isgreater than the first tilt angle. If the signal starts to form localminima or maxima the marking lines start to separate, as can be seen inthe detector signals 96 and 98. The local minima or maxima are anindication of a resolution which does not provide the possibility tomark or print continuous lines in a direction perpendicular to theadvance direction with a high quality.

Therefore, the invention provides a method for analysing the quality ofa marking to be achieved with different tilting angles. A tilting anglereferring to a signal right before the minima or maxima appear can beconsidered an optimal tilting angle.

1-13. (canceled)
 14. A marking apparatus for marking an object,comprising: a marking head having a plurality of receiving spaces forindividual marking devices, wherein the receiving spaces are arranged ina plurality of rows and columns, such that a two-dimensional array ofreceiving spaces is formed, and a driving mechanism for providing arelative movement of the object relative to the marking head in anadvance direction during a marking operation, wherein the marking headis rotatable about an axis extending transversely to the advancedirection, wherein at least one detector device is arranged within therotatable marking head downstream of the receiving spaces in the advancedirection, and a control marking, which has been applied by at least onemarking device arranged in one of the receiving spaces during themovement of the object relative to the marking head, is detectable bythe at least one detector device at different angles of rotation of themarking head.
 15. The marking apparatus of claim 14, wherein the atleast one detector device is movable along a defined movement pathrelative to the receiving spaces of the marking head.
 16. The markingapparatus of claim 14, wherein the at least one detector device ismovable in a transverse direction with regard to the advance direction.17. The marking apparatus of claim 14, wherein the at least one detectordevice is movable along a defined movement path such that it may beplaced in a position in which it is aligned in the advance directionwith at least one of the receiving spaces, at different angles ofrotation of the marking head.
 18. The marking apparatus of claim 14,wherein the at least one detector device is movable along a linearmovement path.
 19. The marking apparatus of claim 14, wherein ameasuring device is provided for determining the position of thedetector device detecting the control marking.
 20. The marking apparatusof claim 14, wherein a processing unit is provided for determining avalue of an angle of rotation based on the detected control marking. 21.The marking apparatus of claim 14, wherein a processing unit is providedfor determining a characteristic of the detected control marking. 22.The marking apparatus of claim 14, wherein a motor is provided forrotating the marking head.
 23. A method for operating a markingapparatus, wherein the marking apparatus comprises a marking head whichis rotatable about an axis extending transversely to an advancedirection the marking head comprises a plurality of receiving spaces forindividual marking devices for marking an object, the receiving spacesbeing arranged in a plurality of rows and columns, such that atwo-dimensional array of receiving spaces is formed, and at least onereceiving space is equipped with a marking device, wherein the methodcomprises the steps: the object is moved relative to the marking head inthe advance direction, and a control marking is applied by the at leastone marking device during the movement of the object relative to themarking head, the control marking is detected by a detector device,which is arranged within the rotatable marking head downstream of the atleast one marking device.
 24. The method of claim 23, wherein thedetector device is moved in a transverse direction relative to theadvance direction and the control marking is detected by the detectordevice during the movement of the detector device in the transversedirection.
 25. The method of claim 23, wherein an angle of rotation ofthe marking head is determined based on the control marking.
 26. Themethod of claim 23, wherein a plurality of receiving spaces arranged inone column is each equipped with a marking device, the marking head isarranged in a tilted position in which the column of marking devices isinclined with regard to the advance direction of the object, the controlmarking is applied by the plurality of marking devices during themovement of the object relative to the marking head, which controlmarking is a wide control bar due to the tilted position of the markinghead, and the control bar is detected by the detector device, which isarranged downstream of the marking devices.